Field of the Invention
The present invention generally relates to a method for controlling creep driving of a vehicle and, more particularly, to a method for implementing creep driving of a vehicle equipped with an Automated Manual Transmission (AMT) or Dual Clutch Transmission configured to apply driving force to an input shaft of the transmission through a dry clutch.
Description of Related Art
As well known to those skilled in the art, an Automated Manual Transmission (AMT) or Dual Clutch Transmission (DCT) that uses a dry clutch is configured to supply driving force from an engine or motor to an input shaft of the transmission via the dry clutch without a torque converter, so the control performance of the dry clutch has a significant influence on take-off and transmission performance of the vehicle.
As for creep driving, the driver controls the dry clutch to follow a certain target creep speed without manipulating an accelerator pedal, in which case the control performance of the dry clutch still has a high influence on a feeling of creep driving and a feeling of acceleration when the vehicle is accelerated right after creep driving.
Generally, a Proportional Integral (PI) controller is used to control the creep driving, and a simple method including calculating proportional and integral control components and combining the components to output a new creep control signal is used for a difference between a target creep speed and a current speed.
However, in the case that the simple PI controller is used to control the creep driving of a vehicle, when the vehicle is driving downhill, the vehicle accelerates due to gravity and may happen to exceed the target creep speed. At this time, even in a situation where the dry clutch has already been completely disengaged and thus the transfer torque actually has become zero, the PI controller keeps accumulating the integral control component in the negative direction because the vehicle speed exceeds the target creep speed. In this situation where the integral control component has been accumulated in the negative direction, if the vehicle reached the end of the slope and needs to be accelerated to drive uphill, a correct integral control component is not reflected in creep control signals until the integral control component having thus far been accumulated in the negative direction is accumulated into zero again, thereby decreasing re-acceleration performance of the vehicle due to delays in increase of creep torque.
Furthermore, while the vehicle repeatedly stops and goes in a traffic jam, a process is repeated where the integral control component having thus far been accumulated remains if the driver stops the vehicle by stepping on the brake, and is accumulated again if the driver starts the vehicle again with creep driving. If the integral control component increases too much, transfer torque of the dry clutch should be excessively controlled when the creep driving is to be resumed, thus causing shock to the dry clutch and causing the vehicle to lurch.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.